CPR is a process by which one or more rescuers may provide chest compressions and ventilation to a patient who has suffered an adverse cardiac event—by popular terms, a heart attack. Chest compressions are considered to be the most important element of CPR during the first five to eight minutes after CPR efforts begin, because chest compressions help maintain circulation through the body and in the heart itself, which is the organ that can sustain the most damage from an adverse cardiac event. Generally, American Heart Association CPR Guidelines define protocols by which a rescuer is to apply the chest compressions in coordination with ventilations. For example, current 2010 AHA Guidelines specify a ratio of 30:2 for compressions to ventilations—i.e., thirty compressions for every two breaths. And compressions are to be performed at a rate of around 100 per minute.
CPR may be performed by a team of one or more rescuers, particularly when the rescuers are professionals such as emergency medical technicians (EMTs) on an ambulance crew. One rescuer can provide the chest compressions and another can time their ventilations of the patient to match the chest compressions according to the appropriate CPR protocol. When professionals such as EMTs provide the care, ventilation is more likely to be provided via a ventilation bag that a rescuer squeezes, than by mouth-to-mouth.
The CPR can be performed in conjunction with providing shocks to the patient from an external defibrillator, including from an automatic external defibrillator (AED) that is designed to be used by laypeople. Such AEDs often provide audible information to rescuers such as “push harder” (when the rescuer is not performing chest compressions forcefully enough), “stop CPR,” “stand back” (because a shock is about to be delivered), and the like. In determining how chest compressions are being performed, certain defibrillators may obtain information from one or more accelerometers (such as in the CPR D PADZ, CPR STAT PADZ, and ONE STEP pads (made by ZOLL MEDICAL of Chelmsford, Mass.) that can be used to compute depths of chest compression, e.g., to determine that the compressions are too shallow to be effective and thus to cause the defibrillator to speak the verbal cue “push header.”
Chest compressions and ventilation may also be provided mechanically. For example, the AUTOPULSE non-invasive cardiac support pump (made by ZOLL MEDICAL of Chelmsford, Mass.) includes a back board and belt that wraps around a patient's chest. A motor in the backboard causes the belt to cycle between tightening and loosening around the patient's chest so as to provide chest compressions automatically and periodically. Automatic ventilation has been provided to people with various respiratory problems by means of devices like a cuirass, in the form of a shell that wraps around a patient's torso and applies negative pressure below their diaphragm, such as in the form of the HAYEK RTX respirator from Medivent International Ltd. of London, UK.